Long chain branched propylene polymer composition

ABSTRACT

The present invention relates to a propylene polymer composition comprising a long chain branched propylene polymer, wherein said propylene polymer composition has a) a crystallization temperature Tc of less than 115° C., b) a melting temperature Tm of less than 155° C. c) a F30 melt strength of from 5.0 to less than 30.0 cN, and d) a V30 melting extensibility of more than 190 mm/s, a process for producing said propylene polymer composition by reactive modification of a propylene polymer in the presence of a peroxide, an article comprising said propylene polymer composition, the use of said propylene polymer composition for producing an article.

The present invention relates to a propylene polymer compositioncomprising a long chain branched propylene copolymer, a process forpreparing such a propylene polymer composition by means of post reactormodification of the propylene copolymer, an article comprising such apropylene polymer composition, the use of such a propylene polymercomposition for the production of an article and the use of such aprocess for preparing a propylene polymer composition comprising a longchain branched propylene polymer for increasing the melt strength of apropylene polymer composition.

BACKGROUND ART

Propylene homopolymers and copolymers are suitable for many applicationssuch as packaging, textile, automotive, laboratory equipment and pipe.These polymers present a variety of properties such as for example highmodulus, tensile strength, rigidity and heat resistance. Theseproperties make polypropylenes very attractive materials in numerousapplications such as for example films, foams, moulded articles orarticles in automotive applications.

Light weight constructions are an everlasting topic in theseapplications, as solutions with higher stiffness are sought in order toreduce the usage of materials This is not only cost driven but also toreduce the consumption of raw materials and reduce the damage to theenvironment. The most relevant approach for reducing material density isfoaming, for which, however, propylene polymers with linear chainstructure are not well suited. Another important feature is thermalresistance. Many applications, especially in the moulding area, requirehigher thermal resistance in order to fill the article with hot food;therefore the heat distortion temperature (HDT) is crucial. Higher HDTis obviously beneficial especially for moulding application especiallyin the field of packaging.

This objective can be reached by subjecting the polypropylene to apost-reactor modification process such as for example a high meltstrength (HMS) process. This process generates branching in thepolypropylene material resulting in long-chain branched polypropylene.The long-chain branching is generally associated with improvedmelt-strength. These long-chain branched polypropylenes are thereforeoften used for making foams.

A challenge within the field of existing long-chain branchedpolypropylenes and their compositions is that their production generallyleads to the formation of gels. Gel formation results in undesirable lowmelt strength in the polypropylene, limited mechanical performance andpoor appearance of the articles based on it. Gel formation is reflectedby the so-called xylene hot insoluble (XHU) fraction. Thus, there is awish to improve polypropylene with high melt strength with respect toits gel content. By such an improvement, the articles obtained whenusing such a polypropylene will have improved and highly desirableproperties such as improved stiffness, higher thermal resistance andsuperior appearance.

WO 2014/0016205 (in the name of BOREALIS AG) describes a high meltstrength (HMS) post-reactor modification process wherein peroxide andbutadiene are used to make long-chain branched polypropylene (b-PP)materials. The long-chain branched polypropylenes in WO 2014/0016205 areused to prepare foams with reduced gel content. For the preparation ofthe long-chain branched polypropylene in WO 2014/0016205 a specificpolypropylene is used as base material.

EP 3 018 153 A1 and EP 3 018 154 A1 also describe a high melt strength(HMS) post-reactor modification process wherein peroxide and butadieneare used to make long-chain branched polypropylene (b-PP) materials forfilm and foam applications. The propylene polymer to be modified in saidhigh melt strength (HMS) post-reactor modification process ispolymerized in the presence of a catalyst system free of phthalates.

It is disclosed for these processes that for obtaining a long chainbranched propylene polymer composition with a desired melt flow rate(MFR) range a base polypropylene material with a very low MFR has to beused for the preparation of the long-chain branched polypropylene, asthe modification process described in these documents generallyincreases the MFR of the long chain branched propylene polymercomposition compared to the base polypropylene material. Some of thedisadvantages of this method are the necessary restriction to a certainMFR range of the base polypropylene and further the limitation to reachany desired MFR of the long-chain branched polypropylene composition.Therefore there still exists a need to improve the properties of thelong-chain branched polypropylene material, more specifically its gelcontent and to improve the mechanical properties such as the stiffnessand thermal resistance of the resultant long-chain branchedpolypropylene compositions.

It has surprisingly been found that by means of a modified high meltstrength (HMS) post-reactor modification process a propylene polymercomposition comprising a long-chain branched propylene copolymer can beproduced which show the desired improvement in heat resistance andmechanical properties. Preferably, a carefully designed reactor madecopolymer of propylene and comonomer units selected from alpha olefinshaving from 4 to 12 carbon atoms which is introduced to said modifiedprocess can contribute to obtaining a propylene polymer composition withsaid properties.

SUMMARY OF THE INVENTION

The present invention relates to a propylene polymer compositioncomprising a long chain branched propylene copolymer, wherein saidpropylene polymer composition has

-   a) a crystallization temperature Tc of less than 115° C.,-   b) a melting temperature Tm of less than 155° C.-   c) a F30 melt strength of from 5.0 to less than 30.0 cN, and-   d) a V30 melting extensibility of more than 190 mm/s.

The present invention further relates to a process for producing apropylene polymer composition comprising the following steps:

-   a) Polymerizing propylene and comonomers selected from alpha-olefins    having from 4 to 12 carbon atoms in the presence of a single site    catalyst system to produce a propylene copolymer;-   b) Recovering the propylene copolymer;-   c) Extruding the propylene copolymer in the presence of a peroxide    for introducing long chain branching into the propylene copolymer;-   d) Recovering the propylene polymer composition.

Further, the present invention relates to an article comprising thepropylene polymer composition as defined above or below

Additionally, the present invention relates to the use of the propylenepolymer composition as defined above or below for the production of anarticle.

Finally, the present invention relates to the use of the process asdefined above or below for increasing the melt strength of a propylenepolymer composition.

Definitions

According to the present invention, the expression “propylenehomopolymer” relates to a polypropylene that consists substantially,i.e. of at least 99.0 wt %, more preferably of at least 99.5 wt %, stillmore preferably of at least 99.8 wt %, like at least 99.9 wt % ofpropylene units. In another embodiment, only propylene units aredetectable, i.e. only propylene has been polymerized.

According to the present invention, the expression “propylene copolymer”relates to a polypropylene which comprises propylene monomer units andcomonomer units, preferably selected from C₄-C₁₂ alpha-olefins. Theamount of comonomer units in the propylene copolymer is at least 0.1 wt%, preferably at least 0.2 wt %, still more preferably at least 0.5 wt%. In the present invention the amount of comonomer units in thepropylene copolymer suitably exceeds 0.5 wt %.

A propylene random copolymer is a copolymer of propylene monomer unitsand comonomer units, in the present invention preferably selected fromC₄-C₁₂ alpha-olefins, in which the comonomer units are distributedrandomly over the polymeric chain. The propylene random copolymer cancomprise comonomer units from one or more comonomers different in theiramounts of carbon atoms. A propylene random copolymer does not includean elastomeric phase.

Percentages are usually given herein as weight-% (wt %) if not statedotherwise.

DETAILED DESCRIPTION OF THE INVENTION

Propylene Polymer Composition

The present invention relates to a propylene polymer compositioncomprising a long chain branched propylene copolymer, wherein saidpropylene polymer composition has

-   a) a crystallization temperature Tc of less than 115° C.,-   b) a melting temperature Tm of less than 155° C.-   c) a F30 melt strength of from 5.0 to less than 30.0 cN, and-   d) a V30 melting extensibility of more than 190 mm/s.

The propylene polymer composition can comprise the long chain branchedpropylene copolymer together with other compounds selected fromadditives and or polymers. The propylene polymer composition preferablycomprises, more preferably consists of the long chain branched propylenecopolymer as only polymeric component and optional additives.

The propylene polymer composition according to the invention preferablyis a propylene copolymer composition.

Illustrative additives to be used in the propylene polymer compositionof the present invention include, but are not limited to, stabilizerssuch as antioxidants (for example sterically hindered phenols,phosphites/phosphonites, sulphur containing antioxidants, alkyl radicalscavengers, aromatic amines, hindered amine stabilizers, or blendsthereof), metal deactivators (for example Irganox® MD 1024), or UVstabilizers (for example hindered amine light stabilizers). Othertypical additives are modifiers such as antistatic or antifogging agents(for example ethoxylated amines and amides or glycerol esters), acidscavengers (for example Ca-stearate), blowing agents, cling agents (forexample polyisobutene), lubricants and resins (for example ionomerwaxes, polyethylene- and ethylene copolymer waxes, Fischer-Tropschwaxes, montan-based waxes, fluoro-based compounds, or paraffin waxes),nucleating agents (for example talc, benzoates, phosphorous-basedcompounds, sorbitoles, nonitol-based compounds or amide-basedcompounds), as well as slip and antiblocking agents (for exampleerucamide, oleamide, talc, natural silica and synthetic silica orzeolites) and mixtures thereof.

Generally the total amount of additives in the propylene polymercomposition is not more than 5.0 wt %, preferably not more than 1.0 wt%, like in the range of 0.005 to 0.995 wt %, more preferably not morethan 0.8 wt %, based on the total weight of the propylene polymercomposition.

Polymers to be used in the propylene polymer composition of the presentinvention preferably include thermoplastic polymers.

Preferably the total amount of additives, polymers and/or combinationsthereof in the propylene polymer composition according to the inventionis not more than 5.0 wt %, more preferably not more than 0.995 wt %,like in the range of 0.005 to 1.0 wt %, based on the total weight of thepropylene polymer composition according to the invention.

The propylene polymer composition preferably does not contain fillersand/or reinforcement agents in an amount exceeding 5.0 wt.-%. In oneembodiment the propylene polymer composition does not contain fillersand/or reinforcement agents.

Although not preferred the propylene polymer composition according tothe invention can further comprise fillers and/or reinforcement agents.Fillers to be used in the long-chain branched polypropylene composition(b-PP-C) according to the invention include, but are not limited totalc, calcium carbonate, calcium sulphate, clay, kaolin, silica, glass,fumed silica, mica, wollastonite, feldspar, aluminium silicate, calciumsilicate, alumina, hydrated alumina such as alumina trihydrate, glassmicrosphere, ceramic microsphere, wood flour, marble dust, magnesiumoxide, magnesium hydroxide, antimony oxide, zinc oxide, barium sulphateand/or titanium dioxide. Reinforcement agents to be used in thepropylene polymer composition according to the invention include, butare not limited to mineral fibers, glass fibers, carbon fibers, organicfibers and/or polymer fibers.

Preferably the total amount of additives, polymers, fillers,reinforcement agents and/or combinations thereof in the propylenepolymer composition according to the invention is not more than 5.0 wt%, more preferably not more than 1.0 wt %, like in the range of 0.005 to0.995 wt %, based on the total weight of the propylene polymercomposition according to the invention.

The propylene polymer composition has a crystallization temperature Tcas determined by DSC of less than 115.0° C., more preferably of 90.0 to114.0° C., still more preferably 95.0 to 112.0° C. and most preferably98.5 to 111.0° C.

Further, the propylene polymer composition has a melting temperature Tmas determined by differential scanning calorimetry (DSC) of less than155.0° C., preferably of 130.0 to 152.5° C., more preferably 132.5 to150.0° C., and most preferably 135.0 to 145.0° C.

Still further, the propylene polymer composition has a F30 melt strengthas determined by the Rheotens method of from 5.0 to less than 30.0 cN,preferably of from 5.5 to 28.0 cN, more preferably of from 6.0 to 26.0cN and most preferably of from 10.0 to 21.0 cN.

Additionally, the propylene polymer composition has a V30 meltingextensibility as determined by the Rheotens method of more than 190mm/s, preferably 200 to 500 mm/s, more preferably 210 to 400 mm/s andmost preferably 215 to 450 mm/s.

The propylene polymer composition preferably has a xylene hot insolubles(XHU) fraction in an amount of less than 1.00%, more preferably in anamount of from 0.05 to 0.95 wt %, still more preferably in an amount offrom 0.08 to 0.90 wt % and most preferably in an amount of 0.10 to 0.80wt %, based on the total weight amount of the propylene polymercomposition.

Further, the propylene polymer composition preferably has a melt flowrate MFR₂ (230° C., 2.16 kg) of 1.0 to 30.0 g/10 min, more preferably of1.2 to 20.0 g/10 min, still more preferably of 1.4 to 15.0 g/10 min, andmost preferably of 2.2 to 12.5 g/10 min.

Additionally the propylene polymer composition preferably has a meltingenthalpy Hm as determined by DSC of less than 105 J/g, more preferablyin the range of from 85 to 102 J/g, still more preferably in the rangeof from 88 to 100 J/g and most preferably in the range of from 88 to 98J/g.

Still further, the propylene polymer composition preferably has a xylenecold solubles (XCS) fraction in an amount of less than 3.0 wt %,preferably of from 0.5 to 2.8 wt %, more preferably of from 0.8 to 2.6wt %, based on the total weight amount of the propylene polymercomposition.

The propylene polymer composition according to the present inventionsurprisingly combines an improved balance of properties of good meltstrength as can been seen in its F30 melt strength and V30 meltingextensibility, a high crystallinity as can be seen in its meltingtemperature, melting enthalpy and crystallization temperature and lowamount of XCS fraction and low gel content illustrated by the low amountof XHU fraction. The propylene polymer composition according to thepresent invention is therefore especially applicable for films, foamsand moulded articles especially in light weight applications, automotiveapplications and packaging applications, such as food packagingapplications.

The propylene polymer composition according to the invention as definedabove or below is prepared a modified high melt strength (HMS)post-reactor modification process in which long chain branching isintroduced into a propylene copolymer.

Process

The present invention further relates to a process for producing apropylene polymer composition comprising the following steps:

-   a) Polymerizing propylene and comonomers selected from alpha-olefins    having from 4 to 12 carbon atoms in the presence of a single site    catalyst system to produce a propylene copolymer;-   b) Recovering the propylene copolymer;-   c) Extruding the propylene copolymer in the presence of a peroxide    for introducing long chain branching into the propylene copolymer;-   d) Recovering the propylene polymer composition.

Thereby, the propylene polymer composition resulting from said processis preferably defined as the propylene polymer composition according tothe invention as defined above or below.

Polymerization of the Propylene Copolymer

The propylene copolymer polymerized in process step a) is a copolymer ofpropylene with at least one comonomer selected from alpha olefins havingfrom 4 to 12 carbon atoms.

Preferred comonomers are comonomers selected from alpha olefins havingfrom 4 to 8 carbon atoms. Especially preferred are comonomers selectedfrom 1-butene and 1-hexene. Mostly preferred is 1-hexene.

The propylene copolymer is preferably a propylene/1-hexene copolymer orpropylene/1-butene copolymer, most preferably a propylene/1-hexenecopolymer.

The propylene copolymer is preferably a propylene random copolymer, i.e.a propylene copolymer with the comonomer(s) as defined above or belowrandomly distributed in the polymeric chain.

The amount of comonomer in the copolymer of propylene is preferably frommore than 0.5 wt % to 10.0 wt %, preferably from 0.8 to 8.0 wt %, stillmore preferably from 1.0 to 6.5 wt % and most preferably from 1.5 to 5.0wt %, based on the total amount of monomer units in the propylenecopolymer.

The propylene copolymer can be produced in a sequential step process,using reactors in serial configuration and operating at differentreaction conditions. As a consequence, each fraction prepared in aspecific reactor can have its own molecular weight distribution and/orcomonomer content distribution depending on the type of propylenecopolymer produced. When the distribution curves (molecular weight orcomonomer content) from these fractions are superimposed to obtain themolecular weight distribution curve or the comonomer contentdistribution curve of the final copolymer, these curves may show two ormore maxima or at least be distinctly broadened when compared withcurves for the individual fractions. Such a copolymer, produced in twoor more serial steps, is called bimodal or multimodal, depending on thenumber of steps. Accordingly the propylene copolymer may be multimodal,like bimodal, in view of the molecular weight and/or comonomer contentdepending on the type of propylene copolymer.

In case the propylene copolymer is of multimodal, like bimodal,character, in view of the comonomer content, it is appreciated that theindividual fractions are present in amounts influencing the propertiesof the material. Accordingly it is appreciated that each of thesefractions is present in an amount of at least 10 wt % based on thepropylene copolymer. Accordingly in case of a bimodal system, inparticular in view of the comonomer content, the split of the twofractions is preferably 40:60 to 60:40, like roughly 50:50.

The propylene polymer fractions in the multimodal or bimodal propylenecopolymer can be a combination of only propylene copolymers which maydiffer in the amount and/or nature of the comonomer(s). The propylenepolymer fractions in the multimodal or bimodal propylene copolymer canbe a combination of propylene homopolymer(s) and propylene copolymer(s).Thereby, if more than one propylene copolymer is present, the propylenecopolymers may differ in the amount and/or nature of the comonomer(s).

Polymerization processes, which are suitable for producing the propylenepolymer are known in the state of the art and comprise at least onepolymerization stage, where polymerization is typically carried out insolution, slurry, bulk or gas phase. Typically the polymerizationprocess comprises additional polymerization stages or reactors. In oneparticular embodiment the process contains at least one bulk reactorzone and at least one gas phase reactor zone, each zone comprising atleast one reactor and all reactors being arranged in cascade. In oneparticularly preferred embodiment the polymerization process comprisesat least one bulk reactor and at least one gas phase reactor arranged inthat order. In some preferred processes the process comprises one bulkreactor and at least two, e.g. two or three gas phase reactors. Theprocess may further comprise pre- and post-reactors. Pre-reactorscomprise typically pre-polymerization reactors. In this kind ofprocesses the use of higher polymerization temperatures is preferred inorder to achieve specific properties of the polymer. Typicaltemperatures in these processes are 70° C. or higher, preferably 80° C.or higher, even 85° C. or higher. The higher polymerization temperaturesas mentioned above can be applied in some or all reactors of the reactorcascade.

A preferred multistage process is a “loop-gas phase”-process, such asdeveloped by Borealis (known as BORSTAR® technology) described e.g. inpatent literature, such as in EP 0 887 379, WO 92/12182, WO 2004/000899,WO 2004/111095, WO 99/24478, WO 99/24479 or in WO 00/68315. A furthersuitable slurry-gas phase process is the Spheripol® process of Basell.

Suitably a specific type of single site catalyst system is used forpolymerizing the propylene polymer. It is especially preferred that thesingle site catalyst system is a supported single site catalyst system,such as a silica supported single site catalyst system. The singlecatalyst system suitably comprises a specific class of metallocenecomplexes in combination with an aluminoxane cocatalyst and a silicasupport. The metallocene catalyst complexes are either symmetrical orasymmetrical. Asymmetrical means simply that the two ligands forming themetallocene are different, that is, each ligand bears a set ofsubstituents that are chemically different. The metallocene catalystcomplexes preferably are chiral, racemic bridged bisindenyl metallocenesin their anti-configuration. The metallocenes preferably are eitherC2-symmetric or C1-symmetric. When they are C1-symmetric they stillmaintain a pseudo-C2-symmetry since they maintain C2-symmetry in closeproximity of the metal center, although not at the ligand periphery. Bynature of their chemistry, both a meso form and a racemic enantiomerpair (in case of C2-symmetric complexes) or anti and syn enantiomerpairs (in case of C1-symmetric complexes) are formed during thesynthesis of the complexes. Thereby, racemic-anti means that the twoindenyl ligands are oriented in opposite directions with respect to thecyclopentadienyl-metal-cyclopentadienyl plane, while racemic-syn meansthat the two indenyl ligands are oriented in the same direction withrespect to the cyclopentadienyl-metal-cyclopentadienyl plane, as shownin the Figure below.

Formula (I), and any sub formulae, are intended to cover both syn- andanti-configurations. Preferred metallocene catalyst complexes are in theanti configuration.

The metallocene catalyst complexes are preferably employed as theracemic-anti isomers. Ideally, therefore at least 95 mol %, such as atleast 98 mol %, especially at least 99 mol % of the metallocene catalystcomplex is in the racemic-anti isomeric form.

In the metallocene catalyst complexes, the following preferences apply.Metallocene catalyst complexes are preferably of formula (I):

M is either Zr or Hf, preferably Zr.

Each X independently is a sigma-donor ligand.

Thus each X may be the same or different, and is preferably a hydrogenatom, a halogen atom, a linear or branched, cyclic or acyclicC₁₋₂₀-alkyl or -alkoxy group, a C₆₋₂₀-aryl group, a C₇₋₂₀-alkylarylgroup or a C₇₋₂₀-arylalkyl group; optionally containing one or moreheteroatoms of Group 14-16 of the periodic table.

The term halogen includes fluoro, chloro, bromo and iodo groups,preferably chloro groups.

The term heteroatoms belonging to groups 14-16 of the periodic tableincludes for example Si, N, O or S.

More preferably, each X is independently a hydrogen atom, a halogenatom, a linear or branched C₁₋₆-alkyl or C₁₋₆-alkoxy group, a phenyl orbenzyl group.

Yet more preferably, each X is independently a halogen atom, a linear orbranched C₁₋₄-alkyl or C₁₋₄-alkoxy group, a phenyl or benzyl group.

Most preferably, each X is independently chlorine, benzyl or a methylgroup.

Preferably, both X groups are the same.

The most preferred options for both X groups are two chlorides, twomethyl or two benzyl groups.

L is a divalent bridge selected from —R′₂C—, —R′₂C—CR′₂—, —R′₂Si—,—R′₂Si—SiR′₂—, —R′₂Ge—, wherein each R′ is independently a hydrogen atomor a C₁-C₂₀-hydrocarbyl group optionally containing one or moreheteroatoms of Group 14-16 of the periodic table or fluorine atoms, oroptionally two R′ groups taken together can form a ring. The termheteroatoms belonging to groups 14-16 of the periodic table includes forexample Si, N, O or S.

Preferably L is —R′₂Si—, ethylene or methylene.

In the formula —R′₂Si—, each R′ is preferably independently aC₁-C₂₀-hydrocarbyl group. The term C₁₋₂₀-hydrocarbyl group thereforeincludes C₁₋₂₀-alkyl, C₂₋₂₀-alkenyl, C₂₋₂₀-alkynyl, C₃₋₂₀-cycloalkyl,C₃₋₂₀-cycloalkenyl, C₆₋₂₀-aryl groups, C₇₋₂₀-alkylaryl groups orC₇₋₂₀-arylalkyl groups or of course mixtures of these groups such ascycloalkyl substituted by alkyl. Unless otherwise stated, preferredC₁₋₂₀-hydrocarbyl groups are C₁₋₂₀-alkyl, C₄₋₂₀-cycloalkyl,C₅₋₂₀-cycloalkyl-alkyl groups, C₇₋₂₀-alkylaryl groups, C₇₋₂₀-arylalkylgroups or C₆₋₂₀-aryl groups.

Preferably, both R′ groups are the same. It is preferred if R′ is aC₁-C₁₀-hydrocarbyl or C₆-C₁₀-aryl group, such as methyl, ethyl, propyl,isopropyl, tertbutyl, isobutyl, C₃₋₈-cycloalkyl, cyclohexylmethyl,phenyl or benzyl, more preferably both R′ are a C₁-C₆-alkyl,C₅₋₆-cycloalkyl or C₆-aryl group, and most preferably both R′ are methylor one is methyl and the other is cyclohexyl. Most preferably the bridgeis —Si(CH₃)₂—.

Each R¹ are independently the same or can be different and are hydrogen,a linear or branched C₁-C₆-alkyl group, a C₇₋₂₀-arylalkyl,C₇₋₂₀-alkylaryl group or C₆₋₂₀-aryl group or an OY group, wherein Y is aC₁₋₁₀-hydrocarbyl group, and optionally two adjacent R¹ groups can bepart of a ring including the phenyl carbons to which they are bonded.

Preferably, each R¹ are independently the same or can be different andare hydrogen, or a linear or branched C₁-C₆-alkyl group, like methyl ortert.-butyl.

It is for example possible that the C₄-phenyl ring is unsubstituted(i.e. all 3 R¹ are hydrogen), or substituted in the para position only,like 4′-tert.-butyl phenyl, or di-substituted in the 3′ and 5′ position,like 3′,5′-dimethylphenyl or 3′,5′-ditert.-butylphenyl.

Furthermore, it is possible that both phenyl rings have the samesubstitution pattern or that the two phenyl rings have differentsubstitution patterns.

Each R² independently are the same or can be different and are a CH₂—R⁸group, with

R⁸ being H or linear or branched C₁₋₆-alkyl group, C₃₋₈-cycloalkylgroup, C₆₋₁₀-aryl group.

Preferably, both R² are the same and are a CH₂—R⁸ group, with R⁸ being Hor linear or branched C₁-C₄-alkyl group, more preferably, both R² arethe same and are a CH₂—R⁸ group, with R⁸ being H or linear or branchedC₁-C₃-alkyl group. Most preferably, both R² are methyl.

R³ is a linear or branched C₁-C₆-alkyl group, C₇₋₂₀-arylalkyl,C₇₋₂₀-alkylaryl group or C₆-C₂₀-aryl group.

R³ is a preferably linear or branched C₁-C₆-alkyl group or C₆₋₂₀-arylgroup, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl,sec.-butyl and tert.-butyl, preferably a linear C₁-C₄-alkyl group, morepreferably a C₁-C₂-alkyl group and most preferably methyl.

R⁴ is a C(R⁹)₃ group, with R⁹ being a linear or branched C₁-C₆-alkylgroup.

Preferably each R⁹ are the same or different with R⁹ being a linear orbranched C₁-C₄-alkyl group, more preferably with R⁹ being the same andbeing a C₁-C₂-alkyl group. Most preferably, R⁴ is a tert.-butyl groupand hence all R⁹ groups are methyl.

In one embodiment R⁵ and R⁶ independently are the same or can bedifferent and are hydrogen or an aliphatic C₁-C₂₀-hydrocarbyl groupoptionally containing one or more heteroatoms from groups 14-16 of theperiodic table of elements, like an alkyl or alkoxy group, e.g. aC₁-C₁₀-alkyl or -alkoxy group.

Preferably, R⁵ and R⁶ independently are the same or can be different andare hydrogen or a linear or branched C₁-C₆ alkyl group, or aC₁-C₆-alkoxygroup.

More preferably, R⁵ and R⁶ independently are the same or can bedifferent and are hydrogen or a linear or branched C₁-C₄-alkyl group ora C₁-C₄-alkoxygroup.

In another embodiment R⁵ and R⁶ can be joined as parts of the 5-memberedring condensed with indenyl ring which is optionally substituted by ngroups R¹⁰, n being from 0 to 4, preferably 0 or 2 and more preferably0;

whereby each R¹⁰ can be the same or different and may be aC₁-C₂₀-hydrocarbyl group, or a C₁-C₂₀-hydrocarbyl radical optionallycontaining one or more heteroatoms belonging to groups 14-16 of theperiodic table of elements; preferably a linear or branched C₁-C₆-alkylgroup.

R⁷ is H or a linear or branched C₁-C₆-alkyl group or an aryl orheteroaryl group having 6 to 20 carbon atoms optionally substituted by 1to 3 groups R¹¹. Preferably, R⁷ is H or an aryl group having 6 to 10carbon atoms optionally substituted by 1 to 3 groups R¹¹, morepreferably R⁷ is H or a phenyl group optionally substituted by 1 to 3groups R¹¹.

In case R⁷ is an optionally substituted aryl group having 6 to 10 carbonatoms, like phenyl, each R¹¹ are independently the same or can bedifferent and are hydrogen, a linear or branched C₁-C₆-alkyl group, aC₇₋₂₀-arylalkyl, C₇₋₂₀-alkylaryl group or C₆₋₂₀-aryl group or an OYgroup, wherein Y is a C₁₋₁₀-hydrocarbyl group.

Preferably, each R¹¹ are independently the same or can be different andare hydrogen, a linear or branched C₁-C₆-alkyl group or C₆₋₂₀-arylgroups or an OY-group, wherein Y is a C₁₋₄-hydrocarbyl group. Morepreferably, each R¹¹ are independently the same or can be different andare hydrogen or a linear or branched C₁-C₄-alkyl group or an OY-group,wherein Y is a C₁₋₄-hydrocarbyl group. Even more preferably, each R¹¹are independently the same or can be different and are hydrogen, methyl,ethyl, isopropyl, tert.-butyl or methoxy, especially hydrogen, methyl ortert.-butyl.

If the aryl group, like the phenyl group is substituted, it ispreferably substituted by 1 or 2 R^(H) groups. More preferably thephenyl group is substituted by 2 groups R¹¹, even more preferably bothR¹¹ groups are the same, like 3′,5′-dimethyl.

Particularly preferred complexes of the invention include:

-   rac-dimethylsilanediyl-bis-[2-methyl-4-(3′5′    dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl] zirconium    dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4-(4′-tert.-butylphenyl)-inden-1-yl][2-methyl-4-(4′-tert.-butylphenyl)-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4-(4′-tert.-butylphenyl)-inden-1-yl][2-methyl-4-phenyl-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4-(3′,5′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3′,5′-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(4′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3′,5′-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3′,5′-dimethylphenyl)-1,5,6,7-tetrahydro-s    indacen-1-yl][2-methyl-4-(3′,5′-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3′,5′-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3′,5′-ditert-butyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]    zirconium dichloride,-   or their Hf-analogues.

For the avoidance of doubt, any narrower definition of a substituentoffered above can be combined with any other broad or narroweddefinition of any other substituent.

Throughout the disclosure above, where a narrower definition of asubstituent is presented, that narrower definition is deemed disclosedin conjunction with all broader and narrower definitions of othersubstituents in the application.

The ligands required to form the complexes and hence catalysts can besynthesized by any process and the skilled organic chemist would be ableto devise various synthetic protocols for the manufacture of thenecessary ligand materials. For Example WO2007/116034 discloses thenecessary chemistry. Synthetic protocols can also generally be found inWO2002/02576, WO2011/135004, WO2012/084961, WO2012/001052,WO2011/076780, WO2015/158790 and WO2018/122134. The examples sectionalso provides the skilled person with sufficient direction.

To form an active catalytic species it is normally necessary to employ acocatalyst as is well known in the art.

In the preferred single site catalyst system a cocatalyst systemcomprising an aluminoxane cocatalyst is used in combination with theabove defined metallocene catalyst complex.

The aluminoxane cocatalyst can be one of formula (II):

where n is from 6 to 20 and R has the meaning below.

Aluminoxanes are formed on partial hydrolysis of organoaluminumcompounds, for example those of the formula AlR₃, AlR₂Y and Al₂R₃Y₃where R can be, for example, C₁-C₁₀-alkyl, preferably C₁-C₅-alkyl, orC₃-C₁₀-cycloalkyl, C₇-C₁₂-arylalkyl or -alkylaryl and/or phenyl ornaphthyl, and where Y can be hydrogen, halogen, preferably chlorine orbromine, or C₁-C₁₀-alkoxy, preferably methoxy or ethoxy.

The resulting oxygen-containing aluminoxanes are not in general purecompounds but mixtures of oligomers of the formula (II).

The preferred aluminoxane is methylaluminoxane (MAO).

Since the aluminoxanes used according to the invention as cocatalystsare not, owing to their mode of preparation, pure compounds, themolarity of aluminoxane solutions hereinafter is based on theiraluminium content.

The cocatalyst system can also comprise a boron containing cocatalyst incombination with the aluminoxane cocatalyst.

Boron containing cocatalysts of interest include those of formula (III)

BY₃  (III)

wherein Y is the same or different and is a hydrogen atom, an alkylgroup of from 1 to about 20 carbon atoms, an aryl group of from 6 toabout 15 carbon atoms, alkylaryl, arylalkyl, haloalkyl or haloaryl eachhaving from 1 to 10 carbon atoms in the alkyl radical and from 6-20carbon atoms in the aryl radical or fluorine, chlorine, bromine oriodine. Preferred examples for Y are fluorine, trifluoromethyl, aromaticfluorinated groups such as p-fluorophenyl, 3,5-difluorophenyl,pentafluorophenyl, 3,4,5-trifluorophenyl and3,5-di(trifluoromethyl)phenyl. Preferred options are trifluoroborane,tris(4-fluorophenyl)borane, tris(3,5-difluorophenyl)borane,tris(4-fluoromethylphenyl)borane, tris(2,4,6-trifluorophenyl)borane,tris(penta-fluorophenyl)borane, tris(3,5-difluorophenyl)borane and/ortris (3,4,5-trifluorophenyl)borane.

Particular preference is given to tris(pentafluorophenyl)borane.

However it is preferred that borates are used, i.e. compounds containinga borate.

These compounds generally contain an anion of formula:

(Z)₄B⁻  (IV)

where Z is an optionally substituted phenyl derivative, said substituentbeing a halo-C₁₋₆-alkyl or halo group. Preferred options are fluoro ortrifluoromethyl. Most preferably, the phenyl group is perfluorinated.

Such ionic cocatalysts preferably contain a weakly-coordinating anionsuch as tetrakis(pentafluorophenyl)borate ortetrakis(3,5-di(trifluoromethyl)phenyl)borate. Suitable counterions areprotonated amine or aniline derivatives such as methylammonium,anilinium, dimethylammonium, diethylammonium, N-methylanilinium,diphenylammonium, N,N-dimethylanilinium, trimethylammonium,triethylammonium, tri-n-butylammonium, methyldiphenylammonium,pyridinium, p-bromo-N,N-dimethylanilinium orp-nitro-N,N-dimethylanilinium.

Preferred ionic compounds which can be used according to the presentinvention include:

tributylammoniumtetra(pentafluorophenyl)borate,

tributylammoniumtetra(trifluoromethylphenyl)borate,

tributylammoniumtetra(4-fluorophenyl)borate,

N,N-dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate,

N,N-dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate,

N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate,

N,N-di(propyl)ammoniumtetrakis(pentafluorophenyl)borate,

di(cyclohexyl)ammoniumtetrakist(pentafluorophenyl)borate,

triphenylcarbeniumtetrakis(pentafluorophenyl)borate,

or ferroceniumtetrakis(pentafluorophenyl)borate.

Preference is given to triphenylcarbeniumtetrakis(pentafluorophenyl)borate,

N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate,

N,N-dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate or

N,N-dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate.

It has been surprisingly found that certain boron containing cocatalystsare especially preferred. Preferred borates therefore comprise thetrityl, i.e. triphenylcarbenium, ion. Thus, the use of Ph₃CB(PhF₅)₄ andanalogues therefore are especially favoured.

Suitable amounts of cocatalyst will be well known to the person skilledin the art.

Preferably, the amount of cocatalyst is chosen to reach below definedmolar ratios.

The molar ratio of Al from the aluminoxane to the metal ion (M)(preferably zirconium) of the metallocene Al/M may be in the range 1:1to 2000:1 mol/mol, preferably 10:1 to 1000:1, and more preferably 50:1to 600:1 mol/mol.

The molar ratio of feed amounts of optional boron (B) to the metal ion(M) (preferably zirconium) of the metallocene boron/M may be in therange 0.1:1 to 10:1 mol/mol, preferably 0.3:1 to 7:1, especially 0.3:1to 5:1 mol/mol.

Even more preferably, the molar ratio of feed amounts of optional boron(B) to metal ion (M) (preferably zirconium) of the metallocene boron/Mis from 0.3:1 to 3:1

The metallocene complex as described above is used in combination with asuitable cocatalyst combination as described above.

The preferred catalyst system is used in supported form. The particulatesupport material used is silica or a mixed oxide such as silica-alumina,in particular silica.

The use of a silica support is preferred. The skilled man is aware ofthe procedures required to support a metallocene catalyst.

Especially preferably, the support is a porous material so that thecomplex may be loaded into the pores of the particulate support, e.g.using a process analogous to those described in WO94/14856, WO95/12622,WO2006/097497 and EP18282666.

The average particle size of the silica support can be typically from 10to 100 However, it has turned out that special advantages can beobtained, if the support has an average particle size from 15 to 80preferably from 18 to 50 The average pore size of the silica support canbe in the range 10 to 100 nm and the pore volume from 1 to 3 mL/g.

Examples of suitable support materials are, for instance, ES757 producedand marketed by PQ Corporation, Sylopol 948 produced and marketed byGrace or SUNSPERA DM-L-303 silica produced by AGC Si-Tech Co. Supportscan be optionally calcined prior to the use in catalyst preparation inorder to reach optimal silanol group content.

The use of these supports is routine in the art.

The catalyst can contain from 10 to 100 μmol of transition metal pergram of silica, and 3 to 15 mmol of Al per gram of silica.

Preparation Steps:

Step a)

In step a) the silica support is reacted with aluminoxane cocatalyst.

Preferably, the reaction is done with the synthesis stoichiometry of Alin the aluminoxane to silica support in the range of 3-12 mmol Al/gSiO₂.

The silica support is preferably calcined before step a) for removingmoisture from the surface thereof. The calcination temperature isnormally in the range of from 200 to 800° C., preferably in the range offrom 400 to 650° C.

The silica support is then suspended in a suitable hydrocarbon solvent,such as toluene. Suspending is done under inert gas atmosphere, e.g.under nitrogen, at a temperature of from 15° C. to 25° C.

The silica/solvent, preferably silica/toluene, suspension is stirred forsome minutes, preferably for 5 to 60 minutes, more preferably from 10 to30 minutes.

Then aluminoxane cocatalyst, preferably MAO (e.g. as a 30 wt % solutionin toluene), is added to the silica/toluene suspension, preferably witha stoichiometry of 3-12 mmol Al/g SiO2.

It is preferred that not all of the aluminoxane cocatalyst is added instep a), but the main part of the total amount of aluminoxanecocatalyst. Thus 75.0 to 97.0 wt %, preferably 77.0 to 95.0 wt %, morepreferably 85.0 to 92.0 wt %, of the total amount of aluminoxanecocatalyst are added in step a).

After addition of the aluminoxane cocatalyst thesilica/solvent/aluminoxane mixture is heated up to a temperature in therange of from 80° C. to 120° C., preferably from 95° C. to 115° C. andmore preferably from 100° C. to 110° C.

The mixture is stirred for some minutes up to several hours, preferablyfrom 60 minutes up to 5 hours, more preferably from 90 minutes up to 3hours, at this temperature.

Afterwards stirring is stopped, the so obtained slurry is allowed tosettle and the mother liquor is removed, e.g. by filtering off ordecantation.

Subsequently the remaining aluminoxane cocatalyst treated silica supportis preferably washed one or more times, e.g. once or twice, morepreferably twice with toluene and optionally one more time with heptaneat elevated temperature in a range of from 70° C. to 115° C., preferablyfrom 80° C. to 110° C. and more preferably from 90° C. to 100° C.

Preferably, the aluminoxane cocatalyst treated silica support issubsequently dried, preferably first at suitable temperatures, e.g. at40 to 80° C., preferably at 50 to 70° C., more preferably at 58 to 62°C., under nitrogen atmosphere and subsequently under vacuum.

Step b)

In step b) the above defined metallocene complex of formula (I) isreacted with aluminoxane cocatalyst in a suitable hydrocarbon solvent,such as toluene.

Preferably, the same hydrocarbon solvent as in step a) is used.

In this step the remaining part of aluminoxane cocatalyst, preferablyMAO (e.g. as a 30 wt % solution in toluene), i.e. 3.0 to 25.0 wt %,preferably 5.0 to 23.0 wt %, more preferably 8.0 to 13.0 wt %, of thetotal amount of aluminoxane cocatalyst are added in step b) to themetallocene complex of formula (I) and the so obtained solution isstirred for several minutes, preferably from 10 to 120 minutes, morepreferably from 20 to 100 minutes and even more preferably from 40 to 80minutes. Stirring is done at room temperature, e.g. at a temperature offrom 15° C. to 25° C., preferably 18° C. to 22° C.

Optional Step c)

To the solution of metallocene/aluminoxane cocatalyst in a suitablehydrocarbon solvent, preferably in toluene, (prepared in step b)optionally the boron containing cocatalyst, like borate cocatalyst, ifpresent in the single site catalyst system, is added to obtain asolution of metallocene complex of formula (I), boron containingcocatalyst and aluminoxane cocatalyst in a suitable hydrocarbon solvent,preferably in toluene.

The boron containing cocatalyst is added in an amount that a boron/Mmolar ratio of feed amounts in the range of 0.1:1 to 10:1 is reached.Preferably, the molar ratio of feed amounts boron/M is in the range of0.3:1 to 7:1, more preferably 0.3:1 to 5.0:1, most preferably 0.3:1 to3:1. M is Hf or Zr, preferably Zr.

The so obtained solution is further stirred for several minutes,preferably from 10 to 120 minutes, more preferably from 20 to 100minutes and even more preferably from 40 to 80 minutes. Stirring is doneat a temperature of from 15° C. to 25° C., preferably 18° C. to 22° C.

Optional Step d)

The solution obtained in step c) is then added to the aluminoxanecocatalyst treated support obtained in step a), yielding the supportedcatalyst system.

Steps c) and d) are applied for single site catalyst systems comprisinga cocatalyst system comprising a boron containing cocatalyst in additionto the aluminoxane cocatalyst. For single site catalyst systemscomprising a cocatalyst system only comprising an aluminoxane cocatalyststeps c) and d) are omitted.

Step e)

In the final step, the so obtained supported catalyst system canoptionally be washed with an appropriate hydrocarbon solvent such astoluene or heptane and is then dried, preferably in vacuum to yield freeflowing powder.

The amounts of silica support, aluminoxane, preferably MAO, optionalboron containing cocatalyst and metallocene depend on the desired abovedefined ratios (Al/M, Al/SiO₂, M/SiO₂, optional boron/M; M being Hf orZr, preferably Zr).

Recovered Propylene Copolymer

The propylene copolymer which is recovered from the polymerization stepin step b) of the process of the invention is herein denoted “recoveredpropylene copolymer” or simply “propylene copolymer”.

The propylene copolymer is preferably a propylene copolymer as describedabove.

Preferably the propylene copolymer has a xylene cold soluble (XCS)fraction measured according to ISO 16152 (25° C.) an amount of less than3.5 wt %, more preferably from 0.2 to 3.0 wt %, still more preferablyfrom 0.3 to 2.5 wt %, based on the total weight amount of the propylenepolymer.

Further, the propylene copolymer preferably has a melt flow rate MFR₂(230° C., 2.16 kg) of from 1.0 to 10.0 g/10 min, more preferably 1.2 to8.0 g/10 min, still more preferably 1.4 to 7.5 g/10 min and mostpreferably 1.5 to 7.0 g/10 min.

The porosity and the specific pore volume of the inventive propylenecopolymer are measured by mercury porosimetry according to DIN 66133 incombination with helium density measurement according to DIN 66137-2.The porosity is calculated by equation (II) as follows:

Porosity [%]=[specific pore volume/(specific porevolume+1/density)]+100  (II)

The porosity of the inventive propylene copolymer is lower than 10.0%,preferably in the range of 0.2 to 9.0%, more preferably in the range of0.4 to 8.0%. The specific pore volume of the inventive propylenecopolymer is generally less than 0.12 cm³/g, preferably less than 0.10cm³/g, more preferably less than 0.08 cm³/g. In some embodiments thespecific pore volume is not detectable.

According to the invention, the median particle size d50 and the top-cutparticle size d95 of the propylene copolymer are measured by sieveanalysis according to ISO 3310 and evaluated according to ISO 9276-2.The median particle size d50 is in the range of from 150 to 1000 μm,preferably 200 to 800 μm, still more preferably 250 to 600 μm and mostpreferably 275 to 500 μm. The top-cut particle size d95 is in the rangeof from 500 to 2500 μm, preferably 550 to 2000 μm, still more preferably600 to 1500 μm and most preferably 650 to 900 μm.

The propylene copolymer can be unimodal or multimodal, in view of themolecular weight distribution and/or in view of the comonomer contentdistribution.

When the propylene copolymer is unimodal with respect to the molecularweight distribution and/or comonomer content, it may be prepared in asingle stage process e.g. as slurry or gas phase process in respectivelya slurry or gas phase reactor.

Preferably, the unimodal propylene copolymer is prepared in a slurryreactor. Alternatively, the unimodal propylene copolymer may be producedin a multistage process using at each stage, process conditions whichresult in similar polymer properties.

The expression “multimodal” or “bimodal” used herein refers to themodality of the polymer, i.e.

-   -   the form of the polymer's molecular weight distribution curve,        which is the graphical representation of the molecular weight        fraction as a function of its molecular weight

or

-   -   the form of the copolymer's comonomer content distribution        curve, which is the graphical representation of the comonomer        content as a function of the molecular weight of the polymer        fractions.

As will be explained above, the polymer fractions of the propylenecopolymer can be produced in a sequential step process, using reactorsin serial configuration and operating at different reaction conditions.As a consequence, each fraction prepared in a specific reactor can haveits own molecular weight distribution and/or comonomer contentdistribution depending on the type of propylene copolymer produced. Whenthe distribution curves (molecular weight or comonomer content) fromthese fractions are superimposed to obtain the molecular weightdistribution curve or the comonomer content distribution curve of thefinal polymer, these curves may show two or more maxima or at least bedistinctly broadened when compared with curves for the individualfractions. Such a copolymer, produced in two or more serial steps, iscalled bimodal or multimodal, depending on the number of steps.Accordingly the propylene copolymer may be multimodal, like bimodal, inview of the molecular weight and/or comonomer content depending on thetype of propylene polymer produced.

In case the propylene copolymer is of multimodal, like bimodal,character, in view of the comonomer content, it is appreciated that theindividual fractions are present in amounts influencing the propertiesof the material. Accordingly it is appreciated that each of thesefractions is present in an amount of at least 10 wt % based on thepropylene copolymer. Accordingly in case of a bimodal system, inparticular in view of the comonomer content, the split of the twofractions is preferably 40:60 to 60:40, like roughly 50:50.

According to one specific embodiment, the propylene copolymer is ofmultimodal in terms of comonomer content, i.e. comprising two or morefractions differing in comonomer content. Preferably, the propylenecopolymer comprises one fraction having a relatively lower content ofcomonomer having been produced in a first reactor, one fraction having arelatively higher content of comonomer having been produced in a secondreactor, and optionally a third fraction having been produced in a thirdreactor. Preferably, the weight ratio of the fraction having arelatively lower content of comonomer having been produced in a firstreactor to the one fraction having a relatively higher content ofcomonomer having been produced in a second reactor optionally togetherwith the third fraction having been produced in a third reactor, whenpresent, is preferably in the range of from 30:70 to 60:40, morepreferably in the range of from 33:67 to 50:50 and most preferably inthe range of from 35:65 to 45:55.

The propylene copolymer is modified during an extrusion step in thepresence of a peroxide in order to introduce long chain branching intothe propylene copolymer in process step c) of the process of theinvention.

Introduction of Long Chain Branching During Extrusion Step

The long-chain branching is introduced into the propylene by a reactivemodification of the propylene copolymer. This reactive modificationprocess is also part of the present invention. The reactive modificationfor producing the long-chain branched propylene copolymer is preferablyperformed by a reaction of the propylene copolymer with a thermallydecomposing free radical-forming agent.

It is especially preferred that for the reactive modification nofunctionally unsaturated compound chosen from:

a) at least one bifunctionally unsaturated monomer and/or polymer or

b) at least one multifunctionally unsaturated monomer and/or polymer or

c) a mixture of (a) and (b)

is present. “Bifunctionally unsaturated or multifunctionallyunsaturated” as used above means the presence of respectively two ormore non-aromatic double bonds. Examples are e.g. divinylbenzene,cyclopentadiene or polybutadiene.

The reactive modification step for producing a long-chain branchedpropylene copolymer preferably comprises the steps of: introducing thepropylene copolymer recovered in process step b) of the process of theinvention into a melt mixing device, further introducing a thermallydecomposing free radical-forming agent such as a peroxide into said meltmixing device and melt mixing the propylene copolymer and the thermallydecomposing free radical-forming agent in said melt mixing device at abarrel temperature in the range of 160 to 280° C., more preferably 170to 270° C. and most preferably 180 to 235° C.

Suitably said melt mixing device is a continuous melt mixing device likefor example a single screw extruder, a co-rotating twin screw extruderor a co-rotating kneader. Preferably, the melt mixing device includes afeed zone, a kneading zone and a die zone. More preferably, a specifictemperature profile is maintained along the screw of the melt-mixingdevice, having an initial temperature T1 in the feed zone, a midtemperature T2 in the kneading zone and a final temperature T3 in thedie zone, all temperatures being defined as barrel temperatures. Barreltemperature T1 (in the feed zone) is preferably in the range of 160 to220° C. Barrel temperature T2 (in the kneading zone) is preferably inthe range of 180 to 260° C. Barrel temperature T3 (in the die zone) ispreferably in the range of 210 to 270° C. The screw speed of the meltmixing device can be adjusted depending on the material characteristics.The man skilled in the art is well familiar with this and can easilydetermine the appropriate screw speed. Generally the screw speed can beadjusted to a range from 100 to 750 rotations per minute (rpm),preferably to a range from 150 to 650 rotations per minute (rpm).Following the melt-mixing step, the resulting long-chain branchedpropylene copolymer melt can be pelletized, for example in an underwaterpelletizer or after solidification of one or more strands in a waterbath, in a strand pelletizer.

It is especially preferred that the propylene copolymer and thethermally decomposing free radical-forming agent are not premixed at alower temperature in a premixing step before being introduced into themelt mixing device. It is further especially preferred that nofunctionally unsaturated compound as described above is added to themelt mixing device.

In the reactive modification for producing a long-chain branchedpropylene copolymer, the propylene copolymer is suitably mixed with 0.40wt % to 4.00 wt % parts per weight (ppw) of peroxide per 100 parts perweight of propylene copolymer, preferably mixed with 0.50 to 3.50 partsper weight (ppw) of peroxide per 100 parts per weight of propylenecopolymer, more preferably in the presence of 0.60 to 3.00 parts perweight (ppw) of peroxide per 100 parts per weight of propylene copolymerand most preferably in the presence of 0.70 to 2.00 parts per weight(ppw) of peroxide per 100 parts per weight of propylene copolymer.

The thermally decomposing free radical-forming agent usually is aperoxide.

For the present process the peroxide is preferably chosen as to have ahalf-time (t_(1/2)) of not more than 6 min at said above defined barreltemperature of 160 to 280° C. Thereby, the half-time is the timerequired to reduce the original peroxide content of a composition by50%, at a given temperature and indicates the reactivity of saidperoxide.

Preferred peroxides are selected from the group of dialkyl peroxides,such as dialkyl peroxydicarbonates. Suitable examples for dialkylperoxydicarbonates are di-(C₂₋₂₀)-alkyl peroxydicarbonates, preferablydi-(C₄₋₁₆)-alkyl peroxydicarbonates, more preferably di-(C₈₋₁₄)-alkylperoxydicarbonates. Especially preferred are di-(2-ethylhexyl)peroxydicarbonate, di-(4-tert-butylcyclohexyl) peroxycarbonate, dicetylperoxydicarbonate, and dimyristyl peroxycarbonate. Especially preferredis dicetyl peroxydicarbonate.

During the extrusion and modification step c) also other components canbe added to the melt mixing device such as the additives and/orpolymeric compounds as described above. These optional components can beintroduced into the melt mixing device via a side feeder for example.

From said extrusion and modification step c) as described above or belowthe propylene polymer composition is recovered.

Recovered Propylene Polymer Composition

The recovered propylene polymer composition of process step d) of theprocess according to the invention preferably has a lower melt flow rateMFR₂ (230° C., 2.16 kg) compared to the recovered propylene polymer ofprocess step b).

This is insofar surprising as in the high melt strength (HMS)post-reactor modification processes described in EP 3 018 153 A1 and EP3 018 154 A1 an increase of the melt flow rate MFR₂ (230° C., 2.16 kg)of the resulting propylene polymer composition compared to the reactorbased propylene polymer has been observed. This surprising findingallows a broader spectrum of MFR ranges of the recovered propylenecopolymer of process step b) and as a consequence milder melt mixingconditions due to the possibility of using propylene copolymers with ahigher MFR.

It is preferred that the recovered propylene polymer compositioncomprises at least 95.0 wt %, more preferably at least 99.0 wt %, mostpreferably at least 99.005 wt %, of the propylene polymer which has beenlong chain branched in process step c).

Preferably the recovered propylene polymer composition of process stepd) of the process according to the invention refers to the propylenepolymer compositions according to the present invention with all theproperties as described above or below.

Article

The present invention further relates to an article comprising thepropylene polymer composition as defined above or below.

The article is preferably selected from films, foams and mouldedarticles especially in light weight applications, automotiveapplications and packaging applications, such as food packagingapplications.

Preferably the article of the invention comprises at least 70.0 wt %,more preferably at least 80.0 wt %, most preferably at least 90.0 wt %,still most preferably at least 95.0 wt %, of the propylene polymercomposition according to the invention. The above given weight percent(wt %) is calculated based on the total of thermoplastic materialcomprised in the article. In a preferred embodiment the article consistsof the propylene polymer composition according to the invention.

The processes for preparing the films, foams and moulded articlescomprising the propylene polymer composition according to the presentinvention are generally known in the art.

Use

The present invention further relates to the use of the propylenepolymer composition as defined above or below for the production of anarticle.

Said article is preferably selected from films, foams and mouldedarticles especially in light weight applications, automotiveapplications and packaging applications, such as food packagingapplications as described above or below.

Finally, the present invention relates to the use of the process asdefined above or below for increasing the melt strength of a propylenepolymer composition.

Preferably, said propylene polymer composition refers to the propylenepolymer composition according to the present invention with all theproperties as described above or below.

EXAMPLES

1. Determination Methods

a) Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and isindicated in g/10 min. The MFR is an indication of the flowability andhence the processability of the polymer. The higher the melt flow rate,the lower the viscosity of the polymer. The MFR₂ of polypropylene isdetermined at a temperature of 230° C. and under a load of 2.16 kg.

b) Particle Size/Particle Size Distribution

A sieve analysis according to ISO 3310 was performed on the polymersamples. The sieve analysis involved a nested column of sieves with wiremesh screen with the following sizes: >20 μm, >32 μm, >63 μm, >100μm, >125 μm, >160 μm, >200 μm, >250 μm, >315 μm, >400 μm, >500 μm, >710μm, >1 mm, >1.4 mm, >2 mm, >2.8 mm. The samples were poured into the topsieve which has the largest screen openings. Each lower sieve in thecolumn has smaller openings than the one above (see sizes indicatedabove). At the base is the receiver. The column was placed in amechanical shaker. The shaker shook the column. After the shaking wascompleted the material on each sieve was weighed. The weight of thesample of each sieve was then divided by the total weight to give apercentage retained on each sieve. The particle size distribution andthe characteristic median particle size d50 as well as the top-cutparticle size d95 were determined from the results of the sieve analysisaccording to ISO 9276-2.

c) XHU Fraction. Gel Content

The xylene hot insoluble (XHU) fraction is determined according to EN579. About 2.0 g of the polymer (m_(p)) are weighted and put in a meshof metal which is weighted, the total weight being represented by(m_(p+m)). The polymer in the mesh is extracted in a soxhlet apparatuswith boiling xylene for 5 hours. The eluent is then replaced by freshxylene and boiling is continued for another hour. Subsequently, the meshis dried and weighted again (m_(XHU+m)). The mass of the xylene hotinsoluble (m_(XHU)) obtained by the formula m_(XHU+m)-m_(m)=m_(XHU) isput in relation to the weight of the polymer (m_(p)) to obtain thefraction of xylene insolubles m_(XHU)/m_(p).

d) F30 Melt Strength and v30 Melt Extensibility

The test described herein follows ISO 16790:2005. The strain hardeningbehaviour is determined by the method as described in the article“Rheotens-Mastercurves and Drawability of Polymer Melts”, M. H. Wagner,Polymer Engineering and Science, Vol. 36, pages 925 to 935. The strainhardening behaviour of polymers is analysed with a Rheotens apparatus(product of Gottfert, Siemensstr.2, 74711 Buchen, Germany) in which amelt strand is elongated by drawing down with a defined acceleration.The Rheotens experiment simulates industrial spinning and extrusionprocesses. In principle a melt is pressed or extruded through a rounddie and the resulting strand is hauled off. The stress on the extrudateis recorded as a function of melt properties and measuring parameters(especially the ratio between output and haul-off speed, practically ameasure for the extension rate).

For the results presented below, the materials were extruded with a labextruder HAAKE Polylab system and a gear pump with cylindrical die(L/D=6.0/2.0 mm). The gear pump was pre-adjusted to a strand extrusionrate of 5 mm/s, and the melt temperature was set to 200° C. The spinlinelength between die and Rheotens wheels was 80 mm. At the beginning ofthe experiment, the take-up speed of the Rheotens wheels was adjusted tothe velocity of the extruded polymer strand (tensile force zero). Thenthe experiment was started by slowly increasing the take-up speed of theRheotens wheels until the polymer filament breaks. The acceleration ofthe wheels was small enough so that the tensile force was measured underquasi-steady conditions. The acceleration of the melt strand drawn downis 120 mm/sec². The Rheotens was operated in combination with the PCprogram EXTENS. This is a real-time data-acquisition program, whichdisplays and stores the measured data of tensile force and drawdownspeed. The end points of the Rheotens curve (force versus pulley rotaryspeed) is taken as the F30 melt strength and drawability values.

e) Xylene Cold Soluble Fraction (XCS, wt %)

The amount of the polymer soluble in xylene is determined at 25.0° C.according to ISO 16152; 5^(th) edition; 2005-07-01.

f) Melting Temperature

The melting temperature, T_(m), is determined by differential scanningcalorimetry (DSC) according to ISO 11357-3 with a TA-Instruments 2920Dual-Cell with RSC refrigeration apparatus and data station. A heatingand cooling rate of 10° C./min is applied in a heat/cool/heat cyclebetween +23 and +210° C. The crystallization temperature (T_(c)) isdetermined from the cooling step while melting temperature (T_(m)) andmelting enthalpy (H_(m)) are being determined in the second heatingstep.

g) Porosity and Specific Pore Volume

The porosity and the specific pore volume of the polymer are measured bymercury porosimetry according to DIN 66133 in combination with heliumdensity measurement according to DIN 66137-2. The samples were firstdried for 3 hours at 70° C. in a heating cabinet then stored in anexsiccator until the measurement. The pure density of the samples wasdetermined on milled powder using helium at 25° C. in a QuantachromeUltrapyknometer 1000-T (DIN 66137-2). Mercury porosimetry was performedon non-milled powder in a Quantachrome Poremaster 60-GT in line with DIN66133.

The porosity is calculated by equation (II) like:

$\begin{matrix}{{{Porosity}\mspace{14mu}\lbrack\%\rbrack} = {\quad{\left\lbrack {{specific}\mspace{14mu}{pore}\mspace{14mu}{{volume}/\left( {{{specific}\mspace{14mu}{pore}\mspace{14mu}{volume}} + \frac{1}{density}} \right)}} \right\rbrack*100}}} & ({II})\end{matrix}$

h) Quantification of Copolymer Microstructure by ¹³C-NMR Spectroscopy

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used toquantify the comonomer content of the polymers.

Quantitative ¹³C{¹H} NMR spectra recorded in the molten-state using aBruker Avance III 500 NMR spectrometer operating at 500.13 and 125.76MHz for ¹H and ¹³C respectively. All spectra were recorded using a ¹³Coptimised 7 mm magic-angle spinning (MAS) probehead at 180° C. usingnitrogen gas for all pneumatics. Approximately 200 mg of material waspacked into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz.This setup was chosen primarily for the high sensitivity needed forrapid identification and accurate quantification (Klimke, K., Parkinson,M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem.Phys. 2006; 207:382.; Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm,M., Macromol. Chem. Phys. 2007; 208:2128.; Castignolles, P., Graf, R.,Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373).Standard single-pulse excitation was employed utilising the NOE at shortrecycle delays of 3s (Pollard, M., Klimke, K., Graf, R., Spiess, H. W.,Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004;37:813.; Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382.) and the RS-HEPTdecoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005,176, 239.; Griffin, J. M., Tripon, C., Samoson, A., Filip, C., andBrown, S. P., Mag. Res. in Chem. 2007 45, S1, S198). A total of 16384(16k) transients were acquired per spectra.

Quantitative ¹³C{¹H} NMR spectra were processed, integrated and relevantquantitative properties determined from the integrals. All chemicalshifts are internally referenced to the methyl isotactic pentad (mmmm)at 21.85 ppm.

Characteristic signals corresponding to the incorporation of 1-hexenewere observed and the comonomer content quantified in the following way.

The amount 1-hexene incorporated in PPHPP isolated sequences wasquantified using the integral of the αH2 sites at 44.2 ppm accountingfor the number of reporting sites per comonomer:

H=Iα/2

With no other signals indicative of other comonomer sequences, i.e.consecutive comonomer incorporation, observed the total 1-hexenecomonomer content was calculated based solely on the amount of isolated1-hexene sequences:

H _(total) =H

The amount of propene was quantified based on the main Sαα methylenesites at 46.7 ppm and compensating for the relative amount of αB2 andααB2B2 methylene unit of propene not accounted for (note B and BB countnumber of butane monomers per sequence not the number of sequences):

P _(total) =I _(s) αα+H

With characteristic signals corresponding to regio defects observed(Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000,100, 1253), the compensation for misinserted propylene units was usedfor Ptotal.

In case of 2,1-erythro mis-insertions presence the signal from ninthcarbon (S_(21e9)) of this microstructure element (Resconi, L., Cavallo,L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253) with chemicalshift at 42.5 ppm was chosen for compensation. In this case:

P _(total) =I _(s) αα+H+3*I(S _(21e9))

The total mole fraction of 1-hexene in the polymer was then calculatedas:

fH=(H _(total)/(H _(total) +P _(total))

The total comonomer incorporation of 1-hexene in mole percent wascalculated from the mole fraction in the usual manner:

H [mol %]=100*fH

The total comonomer incorporation of 1-hexene in weight percent wascalculated from the mole fraction in the standard manner:

H[wt %]=100*(fH*84.17)/((fH*84.17)+((1−fH)*42.08))

2. Preparation of the Propylene Polymers

a) Preparation of the Single Site Catalyst System 1

Catalyst Complex

The catalyst complex used in the polymerization processes for propylenecopolymer PP-1 used for the inventive examples IE1 and IE2 as well asfor comparative example CE1 was:

The metallocene (MC1)(rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy-6-tert-butyl-indenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconiumdichloride) has been synthesized as described in WO 2013/007650, E2.

The catalyst system was prepared using metallocene MC1 and a cocatalystsystem of MAO. The catalyst was supported onto silica.

Preparation of the MAO-Silica Support

A steel reactor equipped with a mechanical stirrer and a filter net wasflushed with nitrogen and the reactor temperature was set to 20° C. Nextsilica grade DM-L-303 from AGC Si-Tech Co, pre-calcined at 600° C. (7.4kg) was added from a feeding drum followed by careful pressuring anddepressurising with nitrogen using manual valves. Then toluene (32.2 kg)was added. The mixture was stirred (40 rpm) for 15 min. Next 30 wt %solution of MAO in toluene (17.5 kg) from Lanxess was added via 12 mmline on the top of the reactor within 70 min. The reaction mixture wasthen heated up to 90° C. and stirred at 90° C. for additional two hours.The slurry was allowed to settle and the mother liquor was filtered off.The MAO treated silica support was washed twice with toluene (32.2 kg)at 90° C., following by settling and filtration. The reactor was cooledoff to 60° C. and the solid was washed with heptane (32.2 kg). FinallyMAO treated SiO₂ was dried at 60° C. for 2 h under nitrogen flow 2 kg/h,pressure 0.3 barg and then for 5 hours under vacuum (−0.5 barg) withstirring at 5 rpm. MAO treated support was collected as a free-flowingwhite powder found to contain 12.7% Al by weight.

Preparation of the Single Site Catalyst System 1:

In a nitrogen filled glovebox, a solution of MAO 0.25 mL (30% wt intoluene, AXION 1330 CA Lanxess) in dry toluene (1 mL) was added to analiquot of metallocene MC1 (30.0 mg, 38 μmol). The mixture was stirredfor 60 minutes at room temperature. Next, the solution was slowly addedto 1.0 g of MAO treated silica prepared as described above, which wasplaced in a glass flask. The mixture was allowed to stay overnight,washed with 5 mL of toluene and was then subjected to vacuum drying for1 hour to yield pink free-flowing powder to yield 1.1 g of the catalystas pink free flowing powder.

The catalyst system 1 has an Al content of 12.5 wt %, a Zr content of0.248 wt % and a molar Al/Zr ratio of 170 mol/mol.

b) Preparation of the Ziegler-Natta Catalyst System 2

The Ziegler-Natta catalyst system used in the polymerization processesfor propylene copolymer PP-1 used for the comparative example CE2 wasprepared as follows: 3.4 litre of 2-ethylhexanol and 810 ml of propyleneglycol butyl mono-ether (in a molar ratio 4/1) were added to a 201reactor. Then 7.8 litre of a 20% solution in toluene of BEM (butyl ethylmagnesium) provided by Crompton GmbH, were slowly added to the wellstirred alcohol mixture. During the addition the temperature was kept at10° C. After addition the temperature of the reaction mixture was raisedto 60° C. and mixing was continued at this temperature for 30 minutes.Finally after cooling to room temperature the obtained Mg-alkoxide wastransferred to a storage vessel.

21.2 g of Mg alkoxide prepared above was mixed with 4.0 mlbis(2-ethylhexyl) citraconate for 5 min. After mixing the obtained Mgcomplex was used immediately in the preparation of the catalystcomponent.

19.5 ml of titanium tetrachloride was placed in a 300 ml reactorequipped with a mechanical stirrer at 25° C. Mixing speed was adjustedto 170 rpm. 26.0 g of the Mg-complex prepared above was added within 30minutes keeping the temperature at 25° C. 3.0 ml of Viscoplex® 1-254 and1.0 ml of a toluene solution with 2 mg Necadd 447™ was added. Then 24.0ml of heptane was added to form an emulsion. Mixing was continued for 30minutes at 25° C., after which the reactor temperature was raised to 90°C. within 30 minutes. The reaction mixture was stirred for a further 30minutes at 90° C. Afterwards stirring was stopped and the reactionmixture was allowed to settle for 15 minutes at 90° C. The solidmaterial was washed 5 times: washings were made at 80° C. under stirringfor 30 min with 170 rpm. After stirring was stopped the reaction mixturewas allowed to settle for 20-30 minutes and followed by siphoning.

Wash 1: washing was made with a mixture of 100 ml of toluene and 1 mldonor

Wash 2: washing was made with a mixture of 30 ml of TiCl4 and 1 ml ofdonor.

Wash 3: washing was made with 100 ml of toluene.

Wash 4: washing was made with 60 ml of heptane.

Wash 5: washing was made with 60 ml of heptane during 10 minutes ofstirring.

Afterwards stirring was stopped and the reaction mixture was allowed tosettle for 10 minutes while decreasing the temperature to 70° C. withsubsequent siphoning, followed by N2 sparging for 20 minutes to yield anair sensitive powder.

c) Polymerization of Propylene Polymer PP-1

Propylene polymer PP-1 has been produced in a Borstar® plant with aprepolymerization reactor, one slurry loop reactor and one gas phasereactor in the presence of the single site catalyst system 1. The feedsand polymerization conditions in the different polymerization conditionsare listed in Table 1.

TABLE 1 Polymerization conditions of PP-1 PP-1 PrepolymerizationTemperature ° C. 25 Pressure kPa 5120 Catalyst feed g/h 8.2 H₂ feed g/h0.10 Loop (Reactor 1) Temperature ° C. 65 Pressure kPa 5079 H₂/C₃ ratiomol/kmol 0.10 C₆/C₃ ratio mol/kmol 45.3 Liquid residence time h 0.37Loop reactor split wt % 37 MFR₂ g/10 min 6.4 C₆ content loop fraction wt% 1.3 GPR (Reactor 2) Temperature ° C. 80 Pressure kPa 2400 H₂/C₃ ratiomol/kmol 1.1 C₆/C₃ ratio mol/kmol 5.0 Polymer residence time h 2.5 GPRreactor split wt% 63 C₆ content GPR fraction wt % 4.3 Polymer propertiesXCS wt % 0.9 MFR₂ g/10 min 5.5 C₆ content wt % 3.2 Tm ° C. 140

d) Polymerization of Propylene Homopolymer PP-2

Propylene polymer PP-2 was produced in a pilot plant with aprepolymerization reactor, one slurry loop reactor and one gas phasereactor. The Ziegler-Natta catalyst system 2 described above was usedalong with triethyl-aluminium (TEAL) as co-catalyst and dicyclo pentyldimethoxy silane (D-donor) as external donor. The co-catalyst to donorratio, the co-catalyst to titanium ratio and the polymerizationconditions are indicated in Table 2.

TABLE 2 Polymerization conditions PP-2 Polymerization Co/ED ratiomol/mol 20.1 Co/Ti ratio mol/mol 367.6 Loop (Reactor 1) Time h 0.5Temperature ° C. 75 MFR₂ g/10 min 5.3 XCS wt. - % 2.0 C₂ content wt. - %0.0 H₂/C₃ ratio mol/kmol 1.1 C₂/C₃ ratio mol/kmol 0 amount wt. - % 43GPR (Reactor 2) Time h 2.0 Temperature ° C. 80 Pressure kPa 2600 MFR₂g/10 min 6.2 C₂ content wt. - % 0.0 H₂/C₃ ratio mol/kmol 15.7 C₂/C₃ratio mol/kmol 0.0 amount wt. - % 57 Polymer properties XCS wt % 1.7MFR₂ g/10 min 5.8 T_(m)(DSC) ° C. 164

e) Properties of the Polymer Powders of PP-1 and PP-2

The reactor-made polymer powders and the polymers of PP-1 and PP-2 havethe following properties as disclosed in Table 3 below.

TABLE 3 Properties of the polymer powders and polymers of PP-1 and PP-2PP-1 PP-2 Powder properties porosity % 1.9 11.5 specific pore volumecm³/g <0.01 0.16 median particle size d50 μm 340 640 top-cut particlesize d95 μm 790 920 Polymer properties Comonomer content wt % 3.2 0 XCSwt % 0.9 2.3 MFR₂ g/10 min 5.5 3.2 T_(m)(DSC) ° C. 140 159

3. Reactive Modification

For the preparation of the propylene polymer compositions of inventiveexamples IE1 and IE2 and Comparative example CE2 the propylene polymersPP-1 and PP-2 were subjected to reactive modification using Perkadox 24L(Dicetyl peroxydicarbonate, commercially available from AkzoNobelPolymer Chemistry) as peroxide. No bifunctional agent was premixed tothe propylene polymers as disclosed e.g. in EP 3 018 153 A1 and EP 3 018154 A1. Instead the propylene polymer and the peroxide were mixedtogether in a melt mixing step with an additive package of antioxidantIrganox B 215 (commercially available from BASF SE), and Calciumstearate and acid scavenger ADK STAB HT (commercially available fromAdeka Palmarole) in a co-rotating twin screw extruder of the typeCoperion ZSK18 having a barrel diameter of 18 mm and an L/D-ratio of 40equipped with a high intensity mixing screw having two kneading zonesand a vacuum degassing setup. A melt temperature profile with initialtemperature T1=180° C. in the feed zone, mid temperature T2=200° C. inthe last kneading zone and a final temperature T3=230° C. in the diezone, all temperatures being defined as barrel temperature, wasselected. The screw speed was set at 400 rpm.

For the preparation of the propylene polymer compositions of comparativeexample CE1 the propylene polymer PP-1 was melt mixed as described abovewithout reactive modification.

Following the melt-mixing step, the resulting polymer melt waspelletized after solidification of the strands in a water bath in astrand pelletizer at a water temperature of 40° C. Reaction conditionsand properties of the resulting propylene polymer compositions aresummarized in Table 4.

TABLE 4 Melt mixing conditions and properties of the propylene polymercompositions CE1 IE1 IE2 CE2 Base polymer powder PP-1 PP-1 PP-1 PP-2Polymer powder wt % 99.7 98.7 98.2 98.2 Antioxidant wt % 0.2 0.2 0.2 0.2Ca-Stearat wt % 0.05 0.05 0.05 0.05 Acid scavenger wt % 0.05 0.05 0.050.05 POX Level wt % 0 0.6 1.5 1.5 Process data Screw speed rpm 400 400400 400 Throughput kg/h 7 7 7 7 Barrel temperature ° C. 200 200 200 200Composition properties MFR₂ g/10 min 12.8 7.8 4.0 4.7 F30 cN 1.8 6.516.2 9.5 v30 mm/s 65 219 246 230 XHU wt % 0.08 0.34 0.34 0.14 XCS wt %0.9 1.0 1.1 1.9 Tm ° C. 140 139 139 166 Tc ° C. 106 105 108 132 Hm J/g92 90 90 117

It can be seen that by means of the simplified reactive modificationprocess propylene polymer compositions comprising a long chain branchedpropylene/1-hexene copolymer can be obtained which shows an improvedbalance of properties in regard of low melting and crystallizationtemperatures and high melt strength. The reactive modification processdecreases the melt flow rate of the propylene polymer composition, whichis especially beneficial for moulding applications as it allows the useof propylene base polymers with higher melt flow rate.

1. A propylene polymer composition comprising a long chain branchedpropylene copolymer, wherein said propylene polymer composition has a) acrystallization temperature Tc of less than 115° C., determined by DSCaccording to ISO 11357-3, b) a melting temperature Tm of less than 155°C., determined by DSC according to ISO 11357-3, c) a F30 melt strengthof from 5.0 to less than 30.0 cN, determined following ISO 16790:2005,and d) a V30 melting extensibility of more than 190 mm/s, determinedfollowing ISO 16790:2005.
 2. The propylene polymer composition accordingto claim 1 having a xylene cold solubles (XCS) fraction in an amount ofless than 3.0 wt %, preferably of from 0.5 to 2.8 wt %, more preferablyof from 0.8 to 2.6 wt %, based on the total weight amount of thepropylene polymer composition, determined at 25° C. according to ISO16152, 5^(th) edition, 2005-07-01.
 3. The propylene polymer compositionaccording to claim 1 having a xylene hot insolubles (XHU) fraction in anamount of less than 1.00%, preferably in an amount of from 0.05 to 0.95wt %, still more preferably in an amount of from 0.08 to 0.90 wt % andmost preferably in an amount of 0.10 to 0.80 wt %, based on the totalweight amount of the propylene polymer composition, determined accordingto EN
 579. 4. The propylene polymer composition according to claim 1having a melt flow rate MFR2 of 1.0 to 30.0 g/10 min, preferably of 1.2to 20.0 g/10 min, still more preferably of 1.4 to 15.0 g/10 min, andmost preferably of 2.2 to 12.5 g/10 min, determined according to ISO1133 at a temperature of 230° C. and a load of 2.16 kg.
 5. A process forproducing a propylene polymer composition according to claim 1comprising the following steps: a) Polymerizing propylene and comonomersselected from alpha-olefins having from 4 to 12 carbon atoms in thepresence of a single site catalyst system to produce a propylenecopolymer; b) Recovering the propylene copolymer; c) Extruding thepropylene copolymer in the presence of a peroxide for introducing longchain branching into the propylene copolymer; d) Recovering thepropylene polymer composition.
 6. The process according to claim 5,wherein the single site catalyst system comprises (i) a metallocenecomplex of formula (I):

wherein M is Zr or Hf each X independently is a sigma-donor ligand, L isa divalent bridge selected from —R′₂C—, —R′₂C—CR′₂—, —R′₂Si—,—R′₂Si—SiR′₂—, —R′₂Ge—, wherein each R′ is independently a hydrogen atomor a C₁-C₂₀-hydrocarbyl group optionally containing one or moreheteroatoms of Group 14-16 of the periodic table or fluorine atoms, oroptionally two R′ groups taken together can form a ring, each R¹ areindependently the same or can be different and are hydrogen, a linear orbranched C₁-C₆-alkyl group, a C₇₋₂₀-arylalkyl, C₇₋₂₀-alkylaryl group orC₆₋₂₀-aryl group or an OY group, wherein Y is a C₁₋₁₀-hydrocarbyl group,and optionally two adjacent R¹ groups can be part of a ring includingthe phenyl carbons to which they are bonded, each R² independently arethe same or can be different and are a CH₂—R⁸ group, with R⁸ being H orlinear or branched C₁₋₆-alkyl group, C₃₋₈-cycloalkyl group, C₆₋₁₀-arylgroup, R³ is a linear or branched C₁-C₆-alkyl group, C₇₋₂₀-arylalkyl,C₇₋₂₀-alkylaryl group or C₆-C₂₀-aryl group, R⁴ is a C(R⁹)₃ group, withR⁹ being a linear or branched C₁-C₆-alkyl group, R⁵ is hydrogen or analiphatic C₁-C₂₀-hydrocarbyl group optionally containing one or moreheteroatoms from groups 14-16 of the periodic table of elements; R⁶ ishydrogen or an aliphatic C₁-C₂₀-hydrocarbyl group optionally containingone or more heteroatoms from groups 14-16 of the periodic table ofelements; or R⁵ and R⁶ can be joined as part of a 5-membered ringcondensed with the indenyl, which is optionally substituted by n groupsR¹⁰, n being from 0 to 4; each R¹⁰ is same or different and may be aC₁-C₂₀-hydrocarbyl group, or a C₁-C₂₀-hydrocarbyl radical optionallycontaining one or more heteroatoms belonging to groups 14-16 of theperiodic table of elements; R⁷ is H or a linear or branched C₁-C₆-alkylgroup or an aryl or heteroaryl group having 6 to 20 carbon atomsoptionally substituted by one to three groups R¹¹, each R¹¹ areindependently the same or can be different and are hydrogen, a linear orbranched C₁-C₆-alkyl group, a C₇₋₂₀-arylalkyl, C₇₋₂₀-alkylaryl group orC₆₋₂₀-aryl group or an OY group, wherein Y is a C₁₋₁₀-hydrocarbyl group,(ii) a cocatalyst system comprising an aluminoxane cocatalyst, and (iii)a silica support.
 7. The process according to claim 5, wherein theamount of comonomer units in the polymerization step a) is from morethan 0.5 wt % to 10.0 wt %, preferably from 0.8 to 8.0 wt %, still morepreferably from 1.0 to 6.5 wt % and most preferably from 1.5 to 5.0 wt%, based on the total amount of monomer units in the propylenecopolymer, determined by quantitative ¹³C-NMR spectroscopy.
 8. Theprocess according to claim 5, wherein the particles of the recoveredpropylene copolymer have a porosity of less than 10.0%, more preferablyof 0.2 to 9.0%, and most preferably of 0.4 to 8.0% and/or a specificpore volume of less than 0.12 cm³/g, more preferably of not more than0.10 cm³/g and most preferably of not more than 0.08 cm³/g, determinedby mercury porosimetry according to DIN 661133 in combination withhelium density measurement according to DIN 66137-2.
 9. The processaccording to claim 5, wherein the particles of the recovered propylenecopolymer has a median particle size d50 of from 150 to 1000 μm,preferably 200 to 800 μm and most preferably 250 to 600 μm and/or a topcut particle size d95 of from 500 to 2500 μm, preferably 550 to 2000 μm,and most preferably 600 to 900 μm, determined by sieve analysisaccording to ISO
 3310. 10. The process according to claim 5, wherein themelt mixing the propylene copolymer and the peroxide are melt mixed in amelt mixing device at a barrel temperature in the range of 160 to 280°C., more preferably 170 to 270° C. and most preferably 180 to 235° C.11. The process according to claim 5, wherein the peroxide has ahalf-time (t_(1/2)) of not more than 6 min at a melt temperature of 160to 280° C. and/or the peroxide is added to the propylene copolymer in anamount of 0.40 wt % to 4.00 wt % parts per weight (ppw) of peroxide per100 parts per weight of propylene copolymer, preferably mixed with 0.50to 3.50 parts per weight (ppw) of peroxide per 100 parts per weight ofpropylene copolymer, more preferably in the presence of 0.60 to 3.00parts per weight (ppw) of peroxide per 100 parts per weight of propylenecopolymer and most preferably in the presence of 0.70 to 2.00 parts perweight (ppw) of peroxide per 100 parts per weight of propylenecopolymer.
 12. The process according to claim 5, wherein the long chainbranching is introduced into the propylene copolymer in the absence of abifunctional long chain branching agent.
 13. The process according toclaim 5, wherein the recovered propylene polymer composition of processstep d) has a lower melt flow rate MFR₂ (230° C., 2.16 kg) compared tothe recovered propylene polymer of process step b).
 14. An articlecomprising the propylene polymer composition according to claim
 1. 15.(canceled)
 16. An article comprising the propylene polymer compositionproduced according to the process according to claim 5.